[exim] Exim not using alternate MX record

Hi

Would anyone know why when mail is sent to the primary MTA, and you get
a message like so

prmail.absa.co.za [169.202.6.84] Connection timed out

or

SMTP error from remote mail server after initial connection: host
prmail.absa.co.za [169.202.6.84]: 421-Microsoft ESMTP MAIL Service,
Version: 6.0.3790.1830 ready at Service not available, closing
transmission channel\n

why is it that Exim does not try the secondary MTA.

root@mail:~# dig mx absa.co.za +short
40 prmail.absa.co.za.
100 secmail.absa.co.za.

Thank in advance.

Kind Regards
Brent Clark